The present invention relates generally to razors and more particularly to disposable safety razor heads having one or more blades mounted in a cartridge.
Advances in disposable blade, wet shaving systems have led to the prevalence of blades being attached to injection molded shaving cartridges, having shaving blades captured between cap and platform portions of the cartridge. These cartridges offer the advantage of precise angular and spatial tolerances relative to the soap bar portion of the platform, in order to obtain optimum shaving results. During manufacture, detailed procedures are undertaken to ensure maintenance of optimal angles and blade depths relative to the cartridge soap bar.
Two tolerances that are important to maintain during cartridge manufacture are the angle of the shaving blade relative to the soap bar and the lateral distance, perpendicular to the blade cutting edge, between the blade and the soap bar. The precision angular alignment is normally maintained by defining an elongated surface on the platform portion of the shaving cartridge that also contains the soap bar. Maintenance of the lateral distance between the blade and soap bar is usually accomplished by relatively precise alignment techniques.
One alignment technique for maintaining the lateral distance between the blade and soap bar involves assembling the cartridges in a jig that maintains the proper spatial relationship between the blade and soap bar. This is usually accomplished by restraining the platform in a jig, placing the blade on the platform in alignment with another portion of the jig and installing the cap on top of the nested blade and platform, so as to capture the blade therebetween. The cap and platform are then bonded to capture the blade permanently. Utilization of assembly jigs complicates manufacture and increases costs. In order further to ensure blade capture, the platform or the cap, or both, often contain locating pins that pass through holes defined by a shaving blade.
Another way of ensuring proper lateral alignment between the soap bar and the blade involves precisely casting the locating pins on either the cap and/or the platform to mate very closely with the blade holes so as to ensure proper lateral alignment. However, all components must then be manufactured to relatively high precision tolerances, which raises manufacturing costs. Rather than attempting to maintain extremely precise manufacturing tolerances in the platform and cap, manufacturers have attempted to effect a compromise by ensuring very precise lateral tolerances in the dimension perpendicular to the blade cutting edge while allowing lateral freedom parallel to the blade cutting edge.
One solution that has been attempted for precise lateral alignment, but with longitudinal freedom, has been to manufacture the platform and cap locating pins with elliptical cross-sections such that the major axis of each elliptical cross-section pin is positioned perpendicular to the blade cutting edge and the minor axis is positioned parallel to the blade cutting edge. The holes defined by the razor blade for passage of the locating pins therethrough are then cut in a circular shape that closely approximates the locating pin major axis diameter. In this manner, precise alignment perpendicular to the cutting edge is maintained, yet a small amount of lateral spacing accommodates small variations in manufactured components.
It is more difficult for a tool and die maker to manufacture molds for elliptical cross-section pins rather than circular cross-section pins, which leads to higher manufacturing costs for molds, and so ultimately for the razor head cartridges. The problems associated with cost effective precision alignment of razor blades within razor head cartridges has also inhibited product development in new areas. There is also a recognized need and desire to purchase disposable razor heads having a convex blade for easier and safer shaving of concave portions of the body, such as underarm areas.
In the past, razor heads have been designed with convex-shaped razor cutting edges, such as U.S. Pat. Nos. 1,342,028, issued on June 1, 1920 and 1,670,309, issued on May 22, 1928. The disclosures of these patents represent a previous generation of razor design wherein a disposable, flexible blade is captured by upper and lower portions that in turn mate with a screw-in handle portion. Razor heads and blades of this nature have generally been superseded by disposable cartridge razor heads because the former do not maintain precise angular relation and lateral positioning of the blade cutting edge, which in turn leads to less close shaves and greater danger of accidental shaving nicks. So far, there have been no commercially successful disposable cartridge head razor systems having curved cutting blades because of difficulties encountered in positioning a blade within a curved cap and platform as well as blade alignment problems associated therewith.